The present invention relates to vessel systems for high pressure chemistry and in particular relates to microwave assisted chemical analysis such as digestion in strong acids, or extraction in organic solvents.
The use of microwave radiation for acid digestion and solvent extraction is generally well established in the industry.
Digestion refers to several types of processes, including reducing materials to ash in a high temperature furnace. In the context of the invention, however, digestion is predominantly carried out by placing a matrix (rocks, plants, soil, food, pharmaceuticals, plastics, metals) in a strong mineral acid or a combination of several strong mineral acids (sulfuric, hydrochloric, phosphoric, nitric) and heating the resulting combination until the acids break down the matrix into elements or ions. At the end of digestion, the result is usually a clear or nearly colorless solution that can be diluted and then tested using one or more quantitative analysis methods.
Microwave assisted closed-vessel extraction reduces solvent usage significantly and in particular can be used to perform a number of extractions using amounts of solvent an order of magnitude smaller than that required for conventional Sierra extractions.
In the digestion context, the most significant advantage of a closed microwave system is the time savings it provides. Microwave digestions can be carried out in less than about an hour as compared to 5-12 (or more) hours for open digestions. Closed microwave systems also permit digestion to take place at temperatures above the boiling points of the acids, while open digestions are limited to the boiling points of the acids. Microwave digestion requires proportionally less acid than open digestions. When carried out properly, microwave digestion prevents loss of corrosive acid fumes and or a corresponding loss of volatile elements. Finally, microwave digestion eliminates the risk of contamination from external sources as compared to open digestion.
For certain purposes, individualized single sample testing is most helpful, but in many contexts, a batch system that will concurrently digest a plurality of similar matrices at the same time will be helpful and efficient. Current examples include, but are not limited to, the Mars 6™ instrument from CEM Corporation (Matthews N.C., US; the assignee of this application).
In the batch context, efficiency can be increased by including more samples in each batch. Thus, currently available batch systems usually incorporate a turntable that will hold up to 12 digestion vessels concurrently. Typically, each vessel is maintained in some type of reinforcing structure to help maintain the vessels in a closed state while the microwave heating step directly drives the reaction to the temperature required to successfully carry out the digestion.
As some partial disadvantages or limitations, however, a number of such systems are limited to fairly small volumes, and many require connected controls to measure temperature and pressure and are limited to a maximum of 12 vessels at a time. The pressure release in most closed microwave vessel systems is usually carried out by opening the lid of the vessel, even if only slightly, and allowing the gases to escape.
Additionally, some of the mechanical systems used to maintain the vessels closed under a desired pressure (and in some cases to dynamically open at a certain pressure limit) require significant mechanical advantage, for example torquing to as much as 60 inch-pounds.
Based on that, a system that incorporates 12 vessels in a batch will require significant effort to close all of the vessels before the batch can be carried out.
Therefore, a need exists for instruments that include a larger number of vessels on the turntable for the batch, in which the vessels can hold at least about hundred milliliters or more, without any connected controls for temperature and pressure measurement, without any metal parts, and while more intentionally controlling the venting of the dynamic pressure seal.